1. Field of the Invention
This invention relates broadly to the field of metal production and casting. More specifically, this invention relates to an improved mold for a continuous casting system that has a longer useful life, improves the uniformity of heat removal, and turns out a better product than conventional continuous casting molds do.
2. Description of the Prior Art
A conventional continuous casting mold includes a number of liner plates, usually made of copper, and outer walls surrounding the liner plates. The liner plates define a portion of the mold that contacts the molten metal during the casting process. Parallel vertically extending cooling water circulation slots or passageways are provided between the outer walls and the liner plates to remove heat from the liner plates. During operation, water is introduced to these slots, usually at the bottom end of the mold, from a water supply via an inlet plenum that is in communication with all of the slots in a liner plate. The cooling effect so achieved causes an outer skin of the molten metal to solidify as it passes through the mold. The solidification is then completed after the semi-solidified casting leaves the mold by spraying additional coolant, typically water, directly onto the casting. This method of metal production is highly efficient, and is in wide use in the United States and throughout the world.
In most continuous casting machines the molten metal is introduced into the mold from a tundish through a refractory nozzle that is submerged within the mold. As a result of the constant introduction of molten metal through the nozzle ports, the shape of the mold, and the cooling effect that is applied by the hofface of the mold, hot metal or molten metal circulation currents form within the mold and, through the well documented heat transfer medium of convection, cause the cooling rate to be uneven over the surface of the hofface. This can cause uneven deterioration of the hofface, and contribute to premature mold failure. It can also impact adversely on the quality of the cast product. One example of this may be found in the operation of funnel-type molds. A funnel-type mold is used to cast a thin slab product, and includes, at the introduction end of the mold, a relatively wide central region, relatively narrow end regions, and transition regions between the central region and the end regions. The refractory nozzle is inserted into the central region, and, it has been found in practice, premature wear and failure of the mold tend to occur at the transition regions. One of the reasons for this premature wear is felt to be that the rush of incoming molten metal that exits the outlets of the immersion nozzle cause the adjacent inner surface of the solidifying product to be reheated, preventing additional cooling from occurring as the skin travels through this area and in some extreme cases, causes reheating and remelting of the skin to occur. That causes the skin to be thinner in those areas surrounding the outlet ports, which in turn raises the surface temperature of the product and the surface temperature of the mold liner. To the inventors' knowledge, no workable solution to this problem has yet been proposed.
It is clear that a need exists for an improved continuous casting mold and method of continuous casting that compensates for the destructive effect of hot metal circulation patterns within the continuous casting mold.